code: def mock_expl(catdog_rgba):
      return Explanation(
          "mock estimator",
          image=catdog_rgba,
          targets=[TargetExplanation(-1, heatmap=np.zeros((7, 7)))],
      )
  
imports: import pytest
  import numpy
  from eli5.base import Explanation, TargetExplanation
  from eli5.formatters.image import format_as_image, heatmap_to_image, expand_heatmap, _validate_heatmap, _update_alpha, _cap_alpha, _overlay_heatmap
  from .utils_image import assert_pixel_by_pixel_equal
label_desc: Use image node_id 18 for calling a global function with example usage: mock_expl(catdog_rgba) and returns: Explanation